ProjectSummary/Abstract Atopicdermatitis(AD)isachronicrelapsinginflammatorydiseaseoftheskin,characterizedbypruritus(severe itchingoftheskin),eczema,andhypersensitivitytoinnocuousenvironmentalsubstances,whichaffects10- 20%ofchildrenworldwide.TheetiologyofADisincompletelyunderstood,butvarioustypesofimmuneor structuralcellsandmultiplecellsignalingpathwaysarethoughttocontributetothedevelopmentofskinlesions andimmunologicalabnormalitiesinAD.Theskinisacomplexorgancontainingalargepopulationofmast cells(MCs)andinnervatedbyanintricatenetworkofabundantsensorynervefibers,including?nociceptors?? sensorynervesthatareactivatedbyharmfulorpotentiallydangerousstimuli.Recentfindingssuggestthat subtypesofnociceptivesensoryneurons,byimportantlyinfluencingspecializedimmunecells,canregulatethe developmentofbothprotectiveandpathogenicresponses.Otherrecentstudieshaveshownthatmouseskin MCsexhibitstrongexpressionofgenesencodingreceptorsintheMas-relatedGprotein-coupledreceptors (MRGPR)family(e.g.,Mrgprb2:thereceptorforthesubstanceP[SP]inthemouse),throughwhichMCsmight uniquelyinteractwithnociceptors.ThecentralhypothesisofthisprojectisthatinteractionsbetweenTrpv1+, Tac1+(i.e.,SP-producing)nociceptorsandMrgprb2+MCsplayacriticalroleinthedevelopmentoftheskin pathologyandimmunologicalabnormalitiesassociatedwithtype2skininflammation.Thishypothesisisbased onthefollowingpreliminaryfindings:(1)TRPV1geneexpressionisincreasedintheskinofADpatients.(2-4) UsingamousemodelofAD,inwhichepicutaneousexposuretoDermatophagoidesfarinaeextract(Derf)and staphylococcalenterotoxinB(SEB)inducesadermatitiswhoseskinpathologyandgeneexpressionpattern aresimilartothoseinhumanAD,wefoundthat:(2)Trpv1+nociceptorsandMCs,aswellasexpressionofthe Tac1gene(encodingtheprecursorforSP),arerequiredfordysregulationofclaudin1structure,development ofAD-likeskinlesions,andproductionofDerf-specificIgG1andIgE;?(3)dermalMCsphysicallyinteractwith skinSP+nociceptors;?and(4)MCsandMrgprb2arerequiredforSP-inducedskininflammation.Wenowwish toextendtheseobservationsandexploretheirtranslationalrelevancebyusingstate-of-the-artgeneticandcell transferstudiesinmicetounderstandthemechanismsofnociceptor/MCcross-talkinthedevelopmentofAD skinpathology,impairedbarrierfunction,andimmunologicalabnormalities,andtouseinnovativeimaging approachestoanalyzeandcomparenociceptor/MCinteractionsinlesionalskinofmiceandinhumanswith AD.Wethinkthattheproposedstudieswillprovidenewinsightsintoskinneuro-immuneinteractionsthatcan influencetype2skininflammation,particularlythosereflectinginteractionsbetweenSP-producingpeptidergic nociceptorsandMCs,bothinamousemodelofADandinlesionalskinofpatientswithAD.Accordingly,our findingshavethepotentialtoidentifynewtherapeutictargetsfortreatingADandperhapsothertype2skin disorders.